its much easier to just exchange cases!! I accidentally discovered that!! If you google how to rebuild zf5 you come across a write up with lots of pics on how to do it, follow it as far as removing the case, and then just switch cases, as long as you have 2 transmissions or 2 cases that start with the same number its doable, I would be reluctant to drill the gas zf to fit the diesel engine I would not feel safe, by switching cases you keep the integrity a strength of the original case, I'm looking into more interchangeability parts, like the input shaft from a newer zf6 which is an 1/8 of an inch wider, and apparently keeps it from breaking,like the old zf5 will post the results.